A catheter equipped with a balloon (balloon catheter) is used for body organ dilation, which is performed for maintaining a luminal space by placing a stent in a stenosed site of a lumen in the living body, such as a blood vessel, the bile duct, the esophagus, the trachea, the urethra, and other organs. Moreover, the catheter is also used for treating ischemic heart diseases or for urethral catheterization for patients having a difficulty in urination.
Accordingly, the balloon catheter is required to have properties including (1) trackability (a property that enables the balloon to move along the tortuous blood vessels and the like), (2) an ability to pass through stenosed sites of blood vessels and the like, (3) an ability to dilate stenosed sites of calcified blood vessels and the like, (4) compliance (an appropriate degree of non-extensibility by which the balloon catheter does not inflate any further once it has dilated up to a desired diameter), (5) a sufficient degree of strength and pressure resistance that enables the balloon catheter to endure the internal pressure or impact caused at the time of balloon dilation, and the like.
Particularly, the balloon portion is required to have compliance, pressure resistance, and flexibility and to be formed of a thin membrane. Materials previously used to fabricate catheter balloon satisfying such properties are polyethylene terephthalate, polyolefins, polyamide.
For example, a known balloon, which is obtained as disclosed in Japanese Application Publication No. 2008-253786 by selecting aliphatic-aromatic polyamide as a base polymer and making the aliphatic polyamide having a short carbon chain into a polymer alloy to improve compliance or pressure resistance, has aromatic rings in the main chain, and hence the pressure resistance and compliance thereof can be improved. However, this balloon is inferior to a balloon made of polyethylene terephthalate (PET) and the flexibility thereof is poorer than that of aliphatic polyamide.
For this reason, Japanese Application Publication No. 2008-253786 discloses a technique relating to a balloon obtained by adding inorganic crystals to the polymer.
Moreover, another technique of improving pressure resistance and flexibility is disclosed in Japanese Application Publication No. 2005-319289. This document discloses a technique of producing a balloon by biaxial stretch blow molding using a block polymer, which includes a polyamide-based hard segment and a glycol-based soft segment, as a material of the balloon membrane such that a calculated elastic modulus under a pressure caused at the time of balloon dilation becomes 1,300 MPa or higher.